They seem like doorway pages however they are

[kokopoko]

Imagine you have inventory from all over the US on your site. You have standard site navigation to a page with a dynamic URL dedicated to Category Subcategory City State. You also have another page that looks exactly the same, but has a static URL such as Condition-Category-Subcategory-City.

You can only reach the static URL page from a sitemap link in the footer of your site. Basically a static URL site running parallel with the dynamic URL site. Imagine pages like this for 500 cities, all categories and subcategories of this niche.

Since the inventory is different on each page, due to different inventory in different cities, are these pages not considered doorway pages and Google will probably be fine with them? Actually Google is fine with them, they are #1 in everything, which boggles my mind.

[goodroi]

Just a few thoughts:
#1 today does not mean they will be #1 tomorrow. Google isn't perfect and there are short term loopholes but it doesn't mean those loopholes are best for your situation.

Rankings are determined by over a 100 factors. Just because something is ranking does not mean you should copy them 100%. Often they are ranking despite a weakness that if fixed would result in even better rankings.

What you see in one serp does not mean it will work in other serps. The competition varies alot from serp to serp not even going to mention personalization.